The casting changes were made after producers "re-conceived" the character of the lead role, reports The Hollywood Reporter.

The show's producers said in a statement: "As we dug deeper into the mythology of Ravenswood, we decided to re-conceive the character of Olivia. Merritt Patterson seemed to be the best choice for the direction the character is now headed."

Elizabeth Whitson has departed the series, while a replacement for the role of Tess is yet to be cast.

Tyler Blackburn - who plays Caleb Rivers in the parent show - will move over to the spinoff when his character travels to the fictitious troubled town of Ravenswood, while Supernatural actor Brett Dier has been cast as Olivia's twin brother.